﻿#if SILVERLIGHT
using System.Collections.Generic;
using System.ComponentModel;

namespace System.Windows
{
    /// <summary>
    /// Provides an implementation so that you can use the
    /// "weak event listener" pattern to attach listeners
    /// for the <see cref="PropertyChanged" /> event.
    /// </summary>
    public class PropertyChangedEventManager
    {
#region Members
        private Dictionary<string, List<WeakReference>> _list;
        private static object SyncLock = new object();
        private static PropertyChangedEventManager _manager = null;
        #endregion

#region Public methods
        /// <summary>
        /// Adds the specified listener to the list of listeners on the specified source.
        /// </summary>
        /// <param name="source">The object with the event.</param>
        /// <param name="listener">The object to add as a listener.</param>
        /// <param name="propertyName">The name of the property that exists on
        /// source upon which to listen for changes.</param>
        public static void AddListener(INotifyPropertyChanged source,
          IWeakEventListener listener,
          string propertyName)
        {
            Instance.PrivateAddListener(source, listener, propertyName);
        }

        /// <summary>
        /// Removes the specified listener from the list of listeners on the
        /// specified source.
        /// </summary>
        /// <param name="source">The object with the event.</param>
        /// <param name="listener">The object to remove as a listener.</param>
        /// <param name="propertyName">The name of the property that exists
        /// on source upon which to listen for changes.</param>
        public static void RemoveListener(INotifyPropertyChanged source,
          IWeakEventListener listener,
          string propertyName)
        {
            Instance.PrivateRemoveListener(source, listener, propertyName);
        }
        #endregion

        /// <summary>
        /// Get the current instance of <see cref="PropertyChangedEventManager"/>
        /// </summary>
        private static PropertyChangedEventManager Instance
        {
            get
            {
                if (_manager == null)
                    _manager = new PropertyChangedEventManager();
                return _manager;
            }
        }

        /// <summary>
        /// Begin listening for the <see cref="PropertyChanged"/> event on
        /// the provided source.
        /// </summary>
        /// <param name="source">The object on which to start listening
        /// for <see cref="PropertyChanged"/>.</param>
        private void StartListening(INotifyPropertyChanged source)
        {
            source.PropertyChanged += new PropertyChangedEventHandler(this.PropertyChanged);
        }

        /// <summary>
        /// Stop listening for the <see cref="PropertyChanged"/> event on the
        /// provided source.
        /// </summary>
        /// <param name="source">The object on which to start listening for
        /// <see cref="PropertyChanged"/>.</param>
        private void StopListening(INotifyPropertyChanged source)
        {
            source.PropertyChanged -= new PropertyChangedEventHandler(this.PropertyChanged);
        }

        /// <summary>
        /// The method that handles the <see cref="INotifyPropertyChanged.PropertyChanged"/> event.
        /// </summary>
        /// <param name="sender">The source of the event.</param>
        /// <param name="args">A <see cref="PropertyChangedEventArgs"/> that
        /// contains the event data.</param>
        private void PropertyChanged(object sender, PropertyChangedEventArgs args)
        {
            List<WeakReference> list;
            if (_list.TryGetValue(args.PropertyName, out list) && list != null)
            {
                // We have the listeners. Deal with them
                foreach (WeakReference item in list)
                {
                    IWeakEventListener eventItem = item.Target as IWeakEventListener;
                    if (eventItem != null && item.IsAlive)
                    {
                        eventItem.ReceiveWeakEvent(this.GetType(), sender, args);
                    }
                }
            }
            else
            {
                Console.WriteLine("WOOT!");
            }
        }

        /// <summary>
        /// Private method to add the specified listener to the list of listeners
        /// on the specified source.
        /// </summary>
        /// <param name="source">The object with the event.</param>
        /// <param name="listener">The object to add as a listener.</param>
        /// <param name="propertyName">The name of the property that exists
        /// on source upon which to listen for changes.</param>
        private void PrivateAddListener(INotifyPropertyChanged source, IWeakEventListener listener, string propertyName)
        {
            lock (SyncLock)
            {
                if (_list == null)
                {
                    _list = new Dictionary<string, List<WeakReference>>();
                }
                WeakReference reference = new WeakReference(listener);
                if (_list.ContainsKey(propertyName))
                {
                    _list[propertyName].Add(reference);
                }
                else
                {
                    List<WeakReference> list = new List<WeakReference>();
                    list.Add(reference);
                    _list.Add(propertyName, list);
                }
                // Now, start listening to source
                StartListening(source);
            }
        }

        /// <summary>
        /// Private method to remove the specified listener from the list of listeners
        /// on the specified source.
        /// </summary>
        /// <param name="source">The object with the event.</param>
        /// <param name="listener">The object to remove as a listener.</param>
        /// <param name="propertyName">The name of the property that exists on
        /// source upon which to listen for changes.</param>
        private void PrivateRemoveListener(INotifyPropertyChanged source, IWeakEventListener listener, string propertyName)
        {
            lock (SyncLock)
            {
                if (_list != null)
                {
                    if (_list.ContainsKey(propertyName))
                    {
                        // Stop responding to changes
                        StopListening(source);
                        // Remove the item from the list.
                        WeakReference reference = null;
                        foreach (WeakReference item in _list[propertyName])
                        {
                            if (item.Target.Equals(listener))
                            {
                                reference = item;
                            }
                        }
                        if (reference != null)
                        {
                            _list[propertyName].Remove(reference);
                        }
                    }
                }
            }
        }
    }
}
#endif